Reducing disengaging height in fluidized powder systems



Patented Dec. 7, 1848 n aanucmc DISENGAGING mixeur` 1N FLUmIzEn Pownrn SYSTEMS George D. Creelman, Cleveland Heights, Ohio, as-

` signor to The M.

W. Kellogg Company, New

York, N. Y., a corporation of Delaware Application June 28, 1946, Serial No. 679,898

This invention relates in general to an improved method and apparatus for edecting contact between finely divided solids and a gas or gaseous mixture, and particularly to improvements in that type of method and apparatus for effecting such contact wherein the iinely divided solids are maintained in a reaction zone in a highly turbulent iluidized state while a stream of gas, vapors, or mixtures thereof is passed upwardly through the reaction zone.

More particularly, the invention is directed to an improved method and apparatus for effecting separation of the finely divided solids from the gas or vapors after the desired degree of contact has been achieved. In general. the .apparatus commonly employed for effecting such contact of gas and powdered material comprises one or more relatively large cylindrical vessels wherein the mass of powder is maintained in a highly turbulent'state in contact with a rising gas stream for a suilicient residence time to eHect the desired chemical or physical changes in vessels generally employed for iluidized powder operations are normaly of a volume considerably greater than that required for the dense iluidized mass of powdered material. This is especially true where it is desired to eiect as complete a separation as possible of the gas and powder within the vessel itself.

Characteristic of fiuidized powder systems of the type contemplated by this invention is the fact that the mass of uidized powdered material within a vessel may be madeto undergo a phase separation comprising two separate and distinct phases or zones. The first of these phases is a relatively denseV turbulent and iluidized mass of particles occupying the lower portion of the vessel and including all but'a substantially minor portion of the powdered solids in the vessel. The second phase is a relatively diffuse or dispersed phase or zone occupying the upper portion of the vessel and including the solid particles that have been lifted from the dense phase by the action of the gas stream passing therethrough.

Between the two phases, that is the dense phase of high powder concentration and the dispersedv phase of low powder concentration. there is a 4relatively narrow, clearly defined zone known as theinterface, wherein the powder concentration changes somewhat abruptly from high to low. The zone immediately above the interface is known as the disengaging zone, wherein solid particles entrained in the vapors rising from the dense phase are disengaged therefrom and are permitted to settle back into the dense bed. In the disengaging zone. that portion of the fiuidized mass which is in excess of the carrying capacity of the gas stream at its minimum velocity in the vessel settles to the interface, where it is returned to the dense phase.

The vertical disengaging distance required above the dense phase may vary within relatively wide limits, dependent upon the nature of the reaction taking place in the vessel, the average particle size of the solids material, and

the linear superficial velocity of the gas stream.

that is, the theoretical linear velocity of the initial gas stream through the vessel without correction for the volume occupied by the solid particles. Normally the necessity for providing sumcient linear gas velocity to maintain the dense bed of solid particles iny a highly turbulent pseudo-liquid condition and the desirability of maintaining a high ratio of contact surface of the solids to volume of the dense phase mass dictates that the solid particles be of extremely small size,.for example, in the order of about forty to four hundred microns for average particle size in the mixture.

Normally such fluidized powder systems are operated at superficial linear velocities and with solid particle sizes such' that entrainment in the rising gas stream is unavoidable, and it is therefore, the usual practice to employ conventional separator means in addition to the disengaging space for removing entrained solid, particles from the gas stream emerging from the dense phase. For example, cyclone separators may be employed forthis purpose within or without the reaction vessel.

In any event, the vertical distance required in the absence of any special means for disengaging th entrained powdered material, roughly approxim tes the diameterof the vessel. The height of the dense phase may vary in accordance with the superficial linear velocity of the gas stream passing upwardly through the vessel and the ratio of gas ,to powder in the feed line leading to the vessel. In systems of the overhead-drawoiI type, wherein all the powdered material and the gas is drawn oil through an outlet in the top of the vessel, and the gas and pow-l der subsequently separated, the height of the dense bed for any given combination of gas and powder is solely a function of the aforementioned variables. In systems of the bottomdrawoil type, however. wherein the dense bed of powdered material is maintained in a highly turbulent suspended state in the rising gas flning of hydrocarbon stream without substantial entralnment therein, and thepowder is drawn oil through an outlet in the bottom of the vessel while the gas leaves the vessel through an outlet overhead,'the height of the dense bed may be controlled independently of the superilcial linear velocity of the gas streamand the ratio of gas to powder in the feed. For example, -a valve in the powder drawoiT line may serve to control the dense bed height by varying the drawoff rate in accordance with conditions in the vessel. In general, Va range of ve to fifteen feet for the height of the dense I bed has been found to be preferable for most It is a primary object of this invention to provide a method and apparatus for effecting contact between finely divided solids and a gas, or gaseous mixture, whereby separation oi.' the powder from Y the gas vis eiected in a minimum period of time relatively narrow vertical paths, whereby the solid particles, which by their random motion are brought into'contact with the surfaces defining said vertical paths, are caused to agglomerate in the comparatively stagnant iilm of gas adjacent said surfaces and to :How downwardly thereaiong4 back into the dense phase.

To attain the foregoing results I dispose a banie having lplurality of parallel vertical pas. sages within the vessel, extending from a point within the interface, or slightly within the dense phase, upwardly to a point adjacent the top of the vessel.

The foregoing and other objects are eil'ected by Y this invention, as will be apparent from the following description and claims taken in connection with the-accompanying drawing forming a part of this application. i While the invention broadly contemplates the novel process and apparatus as being of general application in the chemical processing and oil oils, as exemplined by the well-known uid catalyst-cracking system. 4

Fluid catalyst cracking systems normally employ large reactor and regenerator vessels in which finely divided catalyst powder is contacted vwith a rising stream of gas or gaseous mixture.

In the reactor, thehot catalyst powder is maintained as a dense fiuidized bed while the stream of hydrocarbon vapors is passed upwardly therethrough to effect the desired hydrocarbon conversion. In the regenerator, spent or carbonized catalyst powder which has been withdrawn from the reactor is maintained as a dense iluidized bed while a stream of oxygen-containing gas is passed upwardly therethrough to burn of! the carbon which had been deposited on the catalyst asa contaminant in the reaction zone. In both reactor and regenerator the catalyst powder is separated into a dense phase and a dispersed phase, and in either case it is desirable to disengage the catalyst powder from the hydrocarbon vapors in the dispersed phase in a minimum period oi.' timeor, in lother words. to keep the vertical height of the catalyst disengaging zone as low as possible. v

The invention Awill be more readily understood from Van inspection of the accompanying drawing, in which:

Fig. 1 is a. section in elevation of a vessel in I a fluidized catalytic cracking system embodying an improved baille arrangement dis osed substantially entirely in the dispersedp ase; and Fig. 2 is a, section taken along the line 2-2 of F13. 1. v

Referring to the drawing, the numeral I I represents a. vessel which might be either a regenerator or a reactor, but for the purpose of illustrating the invention it would be considered as being a typical fluid catalyst reactor. Within the vessel I I is a contact zone I2 wherein a mass of iluidized catalyst -is contacted witlr' a stream of hydrocarbon vapors. At a pointadjaccnt the bottom of the vessel an inlet nozzle I3 is provided through which a. mixture of hydrocarbon vapors and powdered catalyst is injected into the contact zone.

Nozzle I3 extends within the contact zone and terminates in a distributor plate I4 by means of which the catalyst-hydrocarbon vapor mixture may be evenly distributed within the dense phase zone. The catalyst-hydrocarbon vapor mixture is pr-eferably introduced into the contacting zone at the desired reaction temperature, which for a cracking operation should be in the range of about 8001050 F. and, preferably. temperatures from about 900-1000 F. may be used. The hydrocarbon stream is supplied under pressure,

`and. preferably in a preheated condition, through conduit I5, connectedto a source not shown. The powdered catalyst is injected into the hydrocarbon stream of conduit I5 through conduit I6, controlled by valve I'I. The powdered catalyst may be supplied as revivied material from a regenerator, not shown. The temperatures of the catalyst in conduit I6 and the hydrocarbon vapors in conduit I5 are so controlled that the mixture thereof in thevv desired catalyst-oil ratio will produce a temperature in the stream injected into refining arts, for afuller understanding yoi? the invention it willhereinafter be particularly described in connection with the iluid catalyst rethe contact zone within the preferred cracking temperature range. The catalyst to oil ratio may be in the order of ve to twenty pounds of catalyst per pound of oil. The injection of the catalysthydrocazbon vapor mixture into the contact zone I2 from distributor Il causes the catalyst to assume a highly turbulent iluidized condition within the vessel. 'I'he catalyst in the con- 5 tact zone undergoes a phase separation, dividing into a dense phase i8 and a dispersed phase Il separated by the interface 20. As previously stated, the level of the interface 2l for an overhead-drawoii system is dependent upon the catalyst-oil ratio in the feed line, the superncia'l linear velocity of the gas stream passing upwardly through the contact zone, and the' kind .of gas and powder. In, a bottom-drawer! system. as illustrated in the drawing, the level of the interface is controlled bythe rate of powder withdrawal.

The interface 20 between the dense phase I8 and the dispersed phase Il! is preferably maintained as a sharply defined narrow zone, in which case it has been found that catalyst entrainment is at 'a minimum. It has been observed that in vessels of large fdiameter the interface is less sharply defined, so that considerable entrainment of the catalyst occurs. Theamount of space required for catalyst deentrainment, therefore, is proportionately large, so that the vessel height is materially increased.

'I'he present invention is concerned with the problem of securing the advantages oi' large vessel diameter within the dense turbulent phase while at the same time acquiring the advantages to be derived from small vessel diameter within the dispersed phase or disengaging zone. y

To this end, I provide a baille 2| within the dispersed phase I9 which comprises a honeycomb or egg-crate type of structure providing a multiplicity of parallel vertical passages 22. The baille 2| extends from a point substantially at the upper level of the dispersed phase to a point near the top of the vessel. Since, under any given set of operating conditions there exists a minimum catalyst concentration which would be attained even with a very great disengaging height, the baille is made of suilicient height to deentrain all the catalyst particles which may normally be returned to the dense bed by this method. The small quantity of fines which normally are not capable oi' separation by this means are carried overhead through the gas outlet 23 and are passed by a conventional separating means, not shown, for separation oi' the gas from the catalyst and complete recovery of the latter.

Since the upper level of the dense phase in an overhead-drawoil system for any given oil and catalyst is determined by the catalyst-oil ratio in the feed line and the superiicial linear gas velocity in the vessel, slight variations in the magnitude of these factors will cause uctuations in the dense phase level, so that, for eilicient operation in view of unavoidable variations which may occur in such systems, it is preferred to have the lower edge of the baille 2| extending a slight distance within the dense phase. In bottom-drawoil systems, however, the dense phase level isdetermined by the rateof catalyst withdrawal, so that it is possible to maintain the dense phase level substantially at the lower edge of the baille. I have illustratedbaie 2| as comprising a plurality of light-gage metal members arranged vertically and parallelly to form a checker-board pattern of iiow paths each of rectangular horizontal cross-section.` It is obvious, however. that:

the provision of a multiplicity of vertical flow paths of relatively small cross-sectional area does not require the particular Vconilguration illus-` trated, and that equally satisfactory results might be obtained withv other arrangements in which a considerable area oi.' vertical path-denning surface is provided. I may, for example, iind 6 it advantageous in a particular application to provide a plurality of vertical tubes in closely nested arrangement with the catalyst stream traveling in contact with the inner tube surfaces, the outer tube surfaces, or both.

At the base of reactor Il a nozzle 24 is pro-r vided through which contaminated catalyst from `the dense phase lil maybe continuously withdrawn ata rate suilicient to maintain the upper level of thedense bed of catalyst at the desired height. A control valve 25 in the outlet conduit 2l may be used to control the catalyst bed level in the contact zone. 'I'he conduit 26 may be connected to the inlet nozzle of a catalyst regenerator, not shown. Since the apparatus required for the proper conditioning of the catalyst and oil prior to injection inthe reaction zone and for the subsequent treatment of the reacted emuents and the contaminated catalyst withdrawn therefrom forms per se no part of the present invention, it is not deemed necessary f ment therewith through the vessel.

By employment of the method and apparatus of this invention, I have found that the usual allowance of a disengaging space above the dense phase approximately equal in height to the diameter of the vessel may be materially lessened. The saving in vertical space may amount to as much as forty percent of that required in the absence of any baille. The savings thus eiected in the overall vessel height are reflected in lowered requirements for supporting structure. The general eompactness in the vessel attained by this invention will result in more economical construcon. l

What I claim is:

1. A process for effecting contact between a finely divided solid contact material and a gas which comprises introducing the finely divided material into a contact zone, passing the gas upwardly through the ilnely` divided material at a velocity adapted to maintain two ,distinct zones of concentration of the finely divided material in said contact zone, said zones being a lower dense phase of pseudo-liquid characteristics and an upper dispersed phase, passing the gas exiting from the top of the dense phase directly through a multiplicity of elongated vertical conned passageways extending upwardly through said second phase, and withdrawing the gas from the contact zone-at an upper portion thereof.

2. A process for effecting contact between a nnely divided solid contact material and a gas lwhich, comprises introducing the iinely divided material and the gas into the lower portion of a contact zone, passing the gas upwardly through the iinely divided material at a velocity adapted to maintain two distinct zones of concentration of the ilnely divided material in said contact zone, said zones being a lower dense phase of pseudo-liquid characteristics and an upper dispersed phase, passing the gas and entrained solids material exiting'from .the top o! the dense phase directly through a multiplicity of elongated relatively narrow channels extending upwardly through said dispersed phase, and withdrawing the gas from the-contact zone at a point adjacent the upper ends of said channels.

3. A process for effecting contact between a finely divided solid contact material and a gas which comprises introducing the finely divided material and the gasinto the lower portion of a contact zone, passing the gas upwardly through the ilnely divided material at a velocity adapted to maintain two distinct zones of concentration of the finely divided material in said contact zone, said zones being a lower dense phase .of pseudo-liquid characteristics and an upper dispersed phase, passing the gas and entrained solids material exiting from the top of the dense phase at substantially unreduced velocity directly through a multiplicity of elongated channels subdividing the cross-section of the entire contact zone and providing for a predetermined vertical distance within said dispersed phase a considerably increased vertical surface contact area for the ilnely divided turbulent particles, withdrawing the gas from the contact zone at a point adjacent the upper ends of said channels, and continuously withdrawing catalyst from the contact zone at a point in the lower portion of said dense phase.

GEORGE DI. CREELMAN.

REFERENCES CITED UNITED STATES PATENTS y Name Date Number v Pier Feb. 16, i932 Melnert et al. -J..- Nov. 12, 1946 'Hemmingel Oct. 3, 1944 

